Visual evoked potentials change as heart rate and carotid pressure change.

The relationship between cardiovascular activity and the brain was explored by recording visual evoked potentials from the occipital regions of the scalp during systolic and diastolic pressure (Experiment I) and during fast and slow heartbeats at systolic and diastolic pressure (Experiment II). Visual evoked potentials changed significantly as heart rate and carotid pressure fluctuated normally, and these changes were markedly different in the right and left cerebral hemispheres. Evoked potentials recorded from the right hemisphere during various cardiac events differed significantly, whereas those recorded from the left did not. In both experiments, differences in the right hemisphere were due primarily to the PI component, which was larger at diastolic than at systolic pressure. The present findings are consistent with formulations from behavioral studies suggesting that baroreceptor activity can influence sensory intake, and suggest that hemispheric specialization may play an important role in the relationship between cardiac events, the brain and behavior. DESCRIPTORS: Carotid pressure. Evoked potentials. Heart rate, Baroreceptors. The early conception that sensory impulses are simply relayed from receptor to cortex was shaken when Granit and Kaada (1952) discovered that the central nervous systetn could control afferent fibers from muscle spindles. Since then, numerous studies have established that the brain can modulate its own sensory input by inhibiting or facilitating sensory transmission anywhere from the peripheral sense organs to the cortical level. In fact, it has been estimated that 10% of all afferent fibers contribute to centrifugal control mechanisms (Livingston, 1976), blurring the classical distinction between "sensory" and "motor" mechanisms. The brainstem reticular formation plays an important role in the centrifugal control of sensory processes. Both electrical stimulation and lesions (Livingston, 1959; Hernandez-Peon, 1961) of the reticuiar formation can facilitate or block interacThese studies represent a portion of a doctoral dissertation submitted by the first author in partial fulfillment of the Ph.D. requirements at Ohio State University. Portions of this report were presented to the Society for Psychophysiological Research in Cincinnati, Ohio, 1979. We are grateful to numerous members of the society for their helpful eomments during that meeting. Address requests for reprints to: Barbara B. Walker, Ann Arbor Veterans Administration Medical Center. 116B. 2215 Fuller Road, Ann Arbor, Michigan 48105. tions occurring at numerous levels of sensory transmission. Since the reticular formation is replete with afferent fibers from the viscera, it seems possible that afferent autonomic activity can also serve to modulate sensory input. There is ample reason to speculate that this is the case, since afferent autonomic fibers are known to exert a variety of extra-homeostatic effects. In the case of the cardiovascular system, for example, stimulation of baroreceptors in the carotid sinus leads to decreased motor activity and prolonged sleep (Koch, 1932), shifts in electrocortical activity from low-voltagefast to high-voltage-slow waves (Bonvallet, Dell. & Hiebel, 1954; Nakao, Ballim, & Gellhorn, 1956), inhibition of evoked monosynaptic reflexes (Bonvallet, Dell, & Hugelin, 1954), suppression of sham rage (Bartorelli. Bizzi, Libretti, & Zanchetti, 1960; Baccelli, Guazzi, Libretti, & Zanchetti, 1965), depression of pyramidal tract cells in the motor cortex (^Coleridge, Coleridge, & Rosenthal, 1976) and single ceil firing to skin stimulation in the nucleus cuneatus (Gahery & Vigier, 1974). and diminished sweat gland and nictitating membrane activity in cats (Horowitz & Kaufman. 1979). It has also been proposed that the inhibition resulting from increases in baroreceptor firing is behavioraily significant (Lacey, 1967). Cardiac acceleration is associated with slower reaction times and © 1982TheSix:icty for Psychophysiotogicai Research. Inc. September, 1982 Visual Evoked Potentials and Cardiac Events 521 impaired visual perception, whereas cardiac deceleration is associated with faster reaction times and enhanced visual perception (Lacey, Kagan, Lacey, & Moss. 1963; Lacey, 1967; Lacey, 1972; DuncanJohnson & Coles, 1974; Sandman, McCanne, Kaiser, & Diamond, 1977). Attempts to relate behavioral changes to differential firing of baroreceptors within a cardiac cycle, however, have yielded equivocal results. Even when faster reaction time or enhanced visual perception has been found early in the cardiac cycle (when baroreceptors fire minimally) compared to late (when baroreceptors fire maximally), the effects have not been robust (Birren, Carden, & Phillips, 1963; Callaway & Layne, 1964; Sandman etal., 1977). In view of these data and the controversy surrounding the behavioral significance of cardiac events (Elliott, 1972; Lacey & Lacey, 1974b; Carroll & Anastasiades, 1978; Obrist, 1976), it is surprising that so few studies have examined the relationship between cardiac events and central nervous system activity in human subjects. Early studies suggested that cardiac events were related to electroencephalographic (EEG) activity (Callaway, 1965; Callaway & Buchsbaum, 1965; Callaway & Layne, 1964), but details of the relationship are difficult to ascertain from these reports. More recently, an experiment from our laboratory demonstrated that average evoked potentials (AEPs) changed as heart rate fluctuated normally (Walker & Sandman, 1979). In this experiment, changes in heart rate were related to the right and left cerebral hemispheres differently, suggesting that hemispheric specialization may play some role in the relationship between cardiac events and behavior. The following experiments were designed to further explore the relationship between cardiac activity and the brain. If baroreceptors are involved in the relationship between cardiac events and behavior, then AEPs recorded at systolic (when baroreceptors fire maximally) and diastolic pressure (when baroreceptors fire minimally) should differ. Specifically, one would expect AEPs to be smaller during systolic pressure than during diastoiic pressure due to the inhibitory effects of baroreceptor stimulation.